This invention relates to sealing means for a rotating shaft, and more particularly to a rotary seal such as a floating seal or a mechanical seal, which is adapted to seal between two relatively rotatable surfaces.
A rotary seal means may comprise, for example, floating seals 5, 5 as shown in FIG. 1, one being arranged on a part of a casing 2 of a rotating shaft 1 but not rotatable, and the other being enclosed by a cover 3 rigidly mounted to the rotating shaft 1. Seal surfaces 6, 6 of the rotatary seal are adapted to rotatably and slidably move when urged by O-rings 4, 4 and springs.
Rotary seals, and especially floating seals used in construction machines or vehicles are subjected to contact with earth, sand, waste water and the like to thus involve severe abrasion. This is also the case with mechanical seals under critical conditions. For this reason, wear proofing is an important problem in rotary seals.
Rotary seals are not always sealed on a given seal surface due to the wobble and runout of the rotating shaft. More specifically, as shown in FIG. 1, the rotary seals 5, 5 are radially out of center when driven. Floating seals are likely to involve a disadvantage due to foreign matter such as particles which may result in abrasion. This is because the positions and contact angles of the seal surfaces 6, 6 vary to provide distorted or offset abrasion by the variation in the working points A and the working forces derived from the depression of the O-rings 4, 4 shown in FIG. 1, so that surface tolerance, that is, the air-tightness of the seal surfaces, may be deteriorated.
For resistance to abrasion in the seal surfaces, alloy cast iron or chilled castings, specifically, Cr-Mo alloy cast iron and white cast iron, have been employed since they normally retain high hardness and are excellent in surface strength. However, these wear resistant cast irons are less machinable by virture of their higher hardness and readily develop casting defects and involve low productivity since they are high alloy castings.
In view thereof, an attempt has been made to provide wear resistant surface treatment to only the seal surfaces which are in need of wear proofing to improve resistance to abrasion at the seal surface, machinability of the base metal, and productivity, but this attempt has failed to obtain a fruitful result. This is because a wear resistant surface treatment layer consisting of a surface coating formed by plating and spraying is susceptible of exfoliation and rupture when foreign matter such as particles are interposed therein. On the other hand, wear resistance treatments involving heat hardening treatments such as boronization and iron nitriding involve difficulties in obtaining a highly hardened layer of sufficient depth and the product often lacks wear resistance. Further, it is impossible with a small-sized product such as a rotary seal to prevent the base metal from being deformed and distorted with heat hardening treatments.
In recent years, surface re-melting techniques have come into the limelight as surface wear resistance treatments. High density energy, specifically, a laser beam, an electron beam, a plasma arc, a TIG arc or the like, each having a thermal convergency of more than 10.sup.4 W/cm.sup.2, is employed to quickly re-melt and cool the surface, to thus obtain a wear resistant structure of extremely high hardness and density. The addition of an alloyed element when remelting brings the capability of forming a deposited alloy layer, so that the wear resistance treatment can obtain products of higher hardness, strength and wear resistance.
The above notwithstanding, the surface re-melting technique limits the base metal to be re-melted as to species. A wider seal surface, as in rotary seals, requires a higher treated area ratio to total product volume. As a result, thermal effects on the rotary seal are not to be disregarded, and involve difficulties in practical use. Distorted or deformed abrasion derived from runout or eccentricity of the rotary seal in itself, as discussed above, is not prevented whatever the wear resistant surface obtained, so that this surface is inevitably subjected to abrasions inherent in the mechanism of the rotary seal.